1. Field of the Invention
The present invention relates to an image forming apparatus equipped with a cleaning device which cleans an endless belt by a blade cleaning system.
2. Related Background Art
Conventionally, as an image forming apparatus, such as a copying machine or a laser beam printer, there has been known a color image forming apparatus adopting a system in which: a toner image formed on an image bearing member, such as a photosensitive drum, is transferred a plurality of times to an intermediate transfer member to form a full color image; and this full color image is then collectively transferred to a recording material, such as paper. Above all, there is widely known a system which is equipped with a plurality of image bearing members for forming toner images of different colors and an intermediate transfer belt in the form of an endless belt constituting the intermediate transfer member and in which this intermediate transfer belt is held in contact with the image bearing members to effect a primary transfer of the toner images of a plurality of colors to the intermediate transfer belt in a superimposing fashion before collectively effecting a secondary transfer of the toner images from the intermediate transfer belt to the recording material.
Incidentally, in a color image forming apparatus using such an intermediate transfer belt, it is necessary to remove toner remaining on the intermediate transfer belt after the secondary transfer of the toner images from the intermediate transfer belt to the recording material. As a cleaning system, a fur brush cleaning system, a blade cleaning system, etc. are available. Of those, a blade cleaning system which uses a plate-like cleaning blade of urethane rubber is widely used because of its simple construction and high cleaning effect. Of those blade cleaning systems, due to its satisfactory cleaning performance, a so-called counter abutment system is in frequent use, in which abutment of the forward end of the cleaning blade is effected in an inclined state such that a downstream side portion of the cleaning blade is at an acute angle with respect to the running direction of the intermediate transfer belt.
It should be noted, however, that, to drive the intermediate transfer belt, it is necessary to use at least a driving roller for transmitting the driving force from the motor to the intermediate transfer belt, and a tension roller for maintaining the requisite tension of the intermediate transfer belt. The intermediate transfer belt is under the largest load where it is in contact with the image bearing members, so it is necessary to arrange the driving roller on the downstream side of the portion where the intermediate transfer belt is in contact with the image bearing members. For, if the driving roller is arranged on the upstream side of the portion where the intermediate transfer belt is in contact with the image bearing members, deflection is likely to be generated in the intermediate transfer belt, and it is necessary to impart a larger tension to the intermediate transfer belt, with the result that the intermediate transfer belt suffers greater damage. Thus, the tension roller is arranged on an upstream side of the portion where the intermediate transfer belt is brought into contact with the image bearing members, and the cleaning device for cleaning the intermediate transfer belt is arranged so as to be opposed to and in contact with the tension roller.
Incidentally, the tension roller serves to impart a fixed tension to the intermediate transfer belt. Thus, the tension roller supports the intermediate transfer belt with a fixed load by urging means, such as a spring. That is, the tension roller is not fixed in position with respect to the apparatus main body, and is under the influence of the peripheral length and unevenness in thickness of the intermediate transfer belt, eccentricity of the tension roller itself and other rollers (e.g., the driving roller), etc., with its position undergoing change every moment. In the case in which the cleaning device adopts the blade cleaning system, inaccuracy in the position of the tension roller, which thus constitutes an opposing roller, leads to a very serious disadvantage.
While the blade cleaning system is an effective system unsurpassed in performance under optimum setting by any other cleaning system, it may often have some adverse effects. For example, when the abutment pressure is too high, the cleaning blade is likely to undergo flutter. Thus, in this system, the permissible range for the abutment pressure of the cleaning blade i.e. the permissible setting range of abutment pressure tends to be smaller as compared with that of other cleaning systems, e.g., the one utilizing a fur brush. Thus, when a roller which undergoes positional fluctuation like the tension roller is used as the opposing roller, it is rather difficult to adopt the blade cleaning system.
If, as means for solving this problem, a construction were adopted in which the cleaning blade is caused to abut the intermediate cleaning blade with a fixed pressure, the blade cleaning system could be adopted relatively easily.
However, for example, when there is a difference in peripheral length between the depth side and the front side of the intermediate transfer belt, the axis of the tension roller is inclined, resulting in generation of generatrix misalignment between the tension roller and the cleaning blade. In particular, use of an intermediate transfer belt whose peripheral length is almost 2 m, the difference in peripheral length between the right and left ends of the intermediate transfer belt is approximately 2 mm at maximum. When such an intermediate transfer belt is used, a positional misalignment of approximately 1 mm at maximum is generated between the right and left sides of the tension roller, causing a generatrix misalignment that is not negligible between the tension roller and the cleaning blade. As a result, the cleaning blade makes unsymmetrical abutment, so that a difference in pressure is generated between the depth side and the front side of the cleaning blade, resulting in unsatisfactory cleaning. As an effective method for solving this problem, there has been conventionally known an effective method in which the cleaning member is provided with an equalizing mechanism, thereby reducing the difference in pressure between the depth side and the front side of the cleaning blade. To realize such a method, a cleaning blade equalizing system has been conceived. In this system, the frictional action of the cleaning blade is always balanced on both sides of an equalizing rotation shaft, so it is possible to apply a blade pressure uniform in the width direction of the image bearing members, making it possible to achieve a satisfactory cleaning performance.
However, once the abutting portion of the cleaning blade is drawn in, the abutment pressure at the portion drawn in becomes larger than that in the other portion, so that the cleaning blade is gradually drawn in, until a wire edge phenomenon occurs to the cleaning blade.